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We have investigated possible mechanisms for conduction in high-T/sub c/ thin-film microbridges biased into the voltage state via the low-frequency noise properties. Measurements on thinned YBCO microbridges indicate that the voltage noise power spectral density S/sub V/(f) is proportional to the DC voltage., Peer Reviewed

We describe results of a study comparing the magnetic field sensitivities of variable thickness bridge (VTB) arrays fabricated in TBCCO, BSCCO, and YBCO thin films. Identical structures were patterned in a variety of films, and the bridges were thinned by four different methods. Analysis of the data yields experimental evidence as to the suitability of these types of films for devices such as the superconducting flux flow transistor (SFFT) which is based on this geometry. The volt-ampere characteristics of the arrays were measured in low uniform magnetic fields (⩽130 G) and in nonuniform fields (⩽5 G) produced by a nearby control line. For these films in this geometry, no measurable effect of the control line magnetic field was observed. Large values of transresistance and current gain could only be attained through a thermal mechanism when the control line was driven normal. Upper bounds for (magnetically generated) transresistance (⩽5 mO) and current gains (⩽0.005) have been inferred from the uniform field data assuming a standard best-case device geometry. All volt-ampere curves followed closely a power law relationship (V~I n), with exponent n ~1.2-10. We suggest materials considerations that may yield improved device performance [-], Peer Reviewed, Postprint (published version)

The noise parameters of a high-temperature superconducting (HTS) flux flow transistor made of TlBaCaCuO operating at 77 K and 3-5 GHz were experimentally determined. It is assumed that the dominant noise mechanism of the device, which is based on an array of weak links with a magnetic control line, is due to the statistical nature of flux nucleation and motion in the links. The noise parameters dictate the dependence of the noise figure on the source impedance, and are calculated by measuring source impedances. Sensitivity analysis is used to estimate the accuracy of the measurements. The measurements indicate a minimum noise figure of less than 1 dB at 3 GHz., Peer Reviewed

The detailed study of factors limiting the performance of microwave monolithic distributed amplifiers utilizing GaAs(Gallium Arsenide) FETS(Field Effect Transistors) is continued. New expressions for gain, attenuation constant, phase constant and optimum numbers of devices are given. A sensitivity analysis is carried out and a computer program to analyze amplifier performance and aid in design is presented. The report concludes with a practical design for an 8-device amplifier from 2 to 20 GHz having a gain of 4.75 dB at 20 GHz. (Author)

Work is continued on the analysis and design of GaAs FET distributed amplifiers. Design tradeoffs are established for type of device, number of devices, gain, impedance level and line cutoff frequency. The procedure for achieving the maximum gain-bandwidth product is detailed. Preliminary work on a broadband 0-360 degrees phase shifter is reported. The design of an integral part of the phase shifter, a distributed paraphase amplifier from 2 - 20 GHz, is presented. (Author)

This report discusses distributed amplifier theory in the context of the microwave monolithic GaAs circuit. It is shown that GaAs FET devices dictate that both the input and output transmission lines become lossy which places fundamental limitations on the distributed amplifier concept and results in different constraints than are found in lossless distributed amplifier design. First order theory indicates that gain asymptotically approaches an upper bound and little benefit results from increasing the number of devices beyond certain limits. (Author)